Responses
No its more like when doing exercise (in this case sex) it needs more oxygen so you breathe through your mouth, if you cover your mouth you’re not getting enough oxygen just from your nose
Sounds valid. Then it must just be my own experience.
I often see this in BL (referencing to chapter 9), that they can't breathe when they close their mouth. So I wonder if it could be that it's considered normal in South Korea or Japan (where the mangas and stuff originate from) that people can't breathe from their nose.